The spiral morphology of Helicobacter pylori appears to confer an advantage to the bacterium in the viscous gastric mucus, since its spiral forms move more effectively in media with high viscosity than more conventional rod-shaped organisms. Peptidoglycans are the stress-bearing structures of bacteria that maintain the integrity of the cell wall and the shape of the bacterium. There is an overall decrease in monomers as the bacteria age, while the percentage of dimers, "anhydro" residues, and dipeptide monomers increases. The lack of detectable trimers or tetramers in H. pylori murein indicates that cross-linking does not occur between three or more glycan chains, whereas cross-linking between three or four glycan chains is detectable in E. coli. The presence of pentapeptide as the main fraction of H. pylori muropeptides indicates that it possesses little carboxypeptidase activity. On the basis of protein sequence homologies, the genome of H. pylori appears to code for homologs of all the enzymes involved in the cytoplasmic synthesis of the disaccharide pentapeptide, starting with the synthesis of UDP-N-acetylmuramic acid and finishing with UDP-disaccharide pentapeptide linked to an undecaprenyl lipid carrier. The second step in building the murein sacculus is the polymerization reaction, accompanied by the insertion of the newly made material into the existing peptidoglycan (PG) layer. Analysis of the H. pylori genome shows the presence of genes coding for all the enzymes of the biosynthetic pathway leading to the disaccharide pentapeptide, which is the basic building block of murein.

General composition and age changes in H. pylori PG. As H. pylori cells age from early to late log phase, the composition of their PG changes. The shaded region represents the amino acids that are removed from the PG in late log phase, essentially resulting in a PG with increased dipeptides.

10.1128/9781555818005/fig14-1_thmb.gif

10.1128/9781555818005/fig14-1.gif

Figure 1

General composition and age changes in H. pylori PG. As H. pylori cells age from early to late log phase, the composition of their PG changes. The shaded region represents the amino acids that are removed from the PG in late log phase, essentially resulting in a PG with increased dipeptides.

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